1. Field of the Invention
The present invention relates to a light-amount controlling apparatus capable of controlling an amount of light received by an optical instrument such as a video camera, and also to a motor employed in this light-amount controlling apparatus.
2. Description of Prior Art
Conventionally, a driving unit of a light-amount controlling apparatus (diaphragm apparatus) assembled into an optical instrument, for instance, a video camera, is in the form of a cylindrical galvanometer. FIG. 8 is an exploded perspective view showing such a conventional galvanometer type diaphragm apparatus. In FIG. 8, reference numeral 24 indicates a base plate for mounting a diaphragm unit and a galvanometer constituting a drive source therefor, reference numeral 37 designates an electromagnetic coil, and reference numeral 33 denotes a bobbin used to wind the electromagnetic coil 37 thereon. Reference numeral 38 represents the same bobbin as the above-described bobbin 33, but no electromagnetic coil is wound on this bobbin 38. Further provided is a magneto rotor 36; a Hall element 34, a yoke 31 used to stabilize magnetic flux; a printed circuit board 35; an upper cover 32, and a screw 39, respectively.
FIG. 9B schematically shows a construction of the cylindrical electromagnetic circuit portion shown in FIG. 8. The outermost diameter of the galvanometer unit corresponds to at least the outer diameter of the yoke 31, namely approximately "2D" with respect to the basic diameter "D" of the magneto rotor 36. As easily seen from FIG. 9B, a dead space "DS" would be produced in such a light-amount controlling apparatus wherein the magneto rotor 36 is driven by way of the electromagnetic coil 37, and the driving speeds of the magneto rotor 36 are controlled by utilizing the Hall element 34. In other words, although the ideal shape of a lens-barrel employed in a video camera and the like is cylindrical, the galvanometer type driving unit of the conventional light-amount controlling apparatus is projected out from the lens-barrel, as illustrated in FIG. 9B.
As to the assembly of the conventional light-amount controlling apparatus, the bobbins 33 and 38 constitute a major element of the magneto rotor 36. Then, members 31, 33, 34, 35, 36, 37, and 38 are incorporated between the base plate 24 and the upper cover 32. The upper cover 32 is screwed to the base plate 24 by a screw 39. Subsequently, a shaft 36a of the magneto rotor 36 is press-fitted, or adhered into a hole 22a of a lever 22, so that the magneto rotor 36 is assembled with the lever 22. Then, a spring 23 is further assembled to the resultant structure, and finally the drive unit is completed. In addition, a windmill type lever 20, diaphragm blades 25, 26, 27, and a cover 28 are attached onto the drive unit.
However, since the galvanometer type driving unit of the conventional light-amount controlling apparatus has a cylindrical shape, there are the following drawbacks:
(1) While a lens (camera) is made compact, even when a diaphragm mechanism unit is stored within a lens cylinder (barrel), the galvanometer type driving unit projects out from the lens cylinder. PA1 (2) Since no damping coil is required in the galvanometer type driving unit for controlling speeds by way of the Hall element, an empty space is necessarily made therein, resulting in a so-called "dead space". PA1 (3) As the magneto rotor is sealed into the electromagnetic coil and the bobbin, both the magnet and the driving lever cannot be formed in an integral body. PA1 (4) As a result of the above-described drawback (3), the driving lever is fitted with the shaft under a certain pressure, or adhered to the shaft by way of a proper adhesive agent. Accordingly, it is very difficult as a practical matter to obtain adherence of the appropriate strength between the driving lever and the shaft. The connection between them may collapse, which would cause problems in the operation of the driving unit. PA1 (5) The driving lever should be properly positioned with respect to the magnetic pole direction of the magnet. Under such circumstances, there is a great fluctuation in the precision with which the driving lever is positioned when it is jointed to the shaft. PA1 (a) The total number of components is large. PA1 (b) The work location is restricted only to the place where the tools are installed. PA1 (c) A large number of working stages are required. PA1 (d) An insufficient screwing condition and a loose screwing condition may occur. PA1 a magneto rotor constructed of a cylindrical permanent magnet, for opening and closing the diaphragm blade by being rotated around a shaft; PA1 an electromagnetic coil; PA1 a magnetic force inducing element for inducing magnetic force in such a manner that the magnetic rotor is sandwiched with maintaining a space by both magnetic poles produced by the electromagnetic coil; PA1 a magnetic force detecting element for detecting the magnetic force produced by the magneto rotor; and PA1 a drive control circuit for setting the magneto rotor to a desired angular position by feeding back thereto the detection result from the magnetic force detecting element, thereby supplying a desired current to the electromagnetic coil. PA1 the first stator having one end from which one magnetic pole of the magnetic force produced by the electromagnetic coil may be induced to an adjacent portion of one side wall of the magneto rotor, and having the other end which penetrates through the electromagnetic coil and projects therefrom; and the second stator having one end from which the other magnetic pole of the magnetic force produced by the electromagnetic coil may be induced to an adjacent portion of the other side wall of the magneto rotor, and having the other end which is abutted to the other end of the first stator, thereby forming a magnetic path. PA1 when the drive control circuit supplies the current to the electromagnetic coil, the magneto rotor may be rotated along a second rotation direction opposite to the first rotation direction. PA1 a circular-shaped bottom plate having an opening at a center thereof, for supporting a diaphragm blade in such a manner that the diaphragm blade can be opened and closed to control an amount of light passing through the opening; PA1 a base plate mounted on the bottom plate, the base plate being arc-shaped in such a manner that the base plate is not projected to the opening and from a circular contour of the bottom plate; PA1 a magneto rotor rotatably supported by the base plate and having a drive means for the diaphragm blade; PA1 a stator positioned and supported by the base plate, whose both poles are located opposite to each other while sandwiching the magneto rotor therewith; PA1 an electromagnetic coil surrounding the stator; and PA1 a cover member positioned and supported by the stator, and having a bearing portion for rotatably supporting the magneto rotor, and a coupling means for coupling the base plate with the cover member. PA1 magnetic force detecting means for detecting magnetic force produced by the magneto rotor; and PA1 drive controlling means for controlling an amount of current supplied to the electromagnetic coil so as to drive the magneto rotor at a predetermined angular position based on the detection result of the magnetic force detecting means. PA1 one end of the first stator may be arranged near the magneto rotor, and the other end of the first stator may be arranged in such a way that the other end thereof is penetrated through the electromagnetic coil and projected therefrom; and PA1 one end of the second stator may be arranged adjacent the magneto rotor, and the other end of the second stator may be arranged in such a manner that the other end thereof is abutted to the other end of the first stator. PA1 a magneto rotor constructed of a cylindrical permanent magnet, for opening and closing the diaphragm blade by being rotated around a shaft; PA1 a magnetic force detecting element for detecting magnetic force generated from the magneto rotor; PA1 an electromagnetic coil for producing magnetic force used to rotate the magneto rotor up to a desired angular position in response to the detection result of the magnetic force detecting element; PA1 a base plate for assembling at least the magneto rotor and the electromagnetic coil in an arc shape in such a manner that the magneto rotor and the electromagnetic coil can be stored a long an inner wall of a lens barrel; and PA1 a bottom plate separably formed with the base plate in an integral form, for storing the diaphragm blade into the lens barrel. PA1 a stator having a first major magnetic pole and a second major magnetic pole, which sandwich a gap; PA1 a field coil wound on the stator; PA1 a permanent magneto rotor rotatably supported within the gap, for opening and closing the diaphragm blade; PA1 auxiliary magnetic poles for exerting detent torque in a direction along which detent torque exerted by the stator and given to the permanent magneto rotor is canceled by the first-mentioned detent torque; PA1 a control unit for properly supplying a current to the field coil so as to rotate the permanent magneto rotor within the gap in either a clockwise direction, or a counter-clockwise direction; and PA1 wherein the detent torque given by the auxiliary magnetic poles to the permanent magneto rotor is made smaller than the detent torque given by the major magnetic poles to the permanent magneto rotor. PA1 the auxiliary magnetic poles may be arranged in such a manner that the auxiliary magnetic poles are positioned opposite to the permanent magneto rotor to define a space similar to the preselected space at a position shifted by 90.degree. with respect to a rotation direction of the permanent magneto rotor; and PA1 a facing area defined between the auxiliary magnetic poles and the permanent magneto rotor may be made smaller than a facing area defined by the major magnetic poles and the permanent magneto rotor. PA1 the auxiliary magnetic poles may be arranged in such a manner that the auxiliary magnetic poles are located opposite to each other while keeping a facing area similar to the facing area defined by the major magnetic poles and the permanent magneto rotor at a position shifted by 90.degree. with respect to a rotation direction of the permanent magneto rotor; and PA1 the space defined between the auxiliary magnetic poles and the permanent magneto rotor may be made larger than the space defined between the major magnetic poles and the permanent magneto rotor. PA1 (1) The magnet, the shaft and the driving lever can be made in an integral body due to the newly developed magneto rotor. That is, the magnet, shaft and driving lever may be constructed in an integral body by using the same material, for instance, the molding materials employed in an ferrite magnet, resulting in a single component, although conventionally the magnet, the shaft, and the driving arm are made of separate materials and are conventionally assembled. As a consequence, the diaphragm unit may be made compact and also the "dead space" could be effectively eliminated. PA1 (2) Since the arc-shaped structure is introduced, the lens cylinder for a video camera and the like may be made compact. PA1 (3) As previously described, since the relevant components could be made in an integral body, higher positioning precision can be assured. Accordingly, this may solve the conventional problems of deteriorated performance and instability caused by positional shifts between the driving arm and the magnet. PA1 (4) Since the driving force is produced from the electromagnetic coil, the structure of the bobbin may be made with a simple shape. Moreover, this bobbin may be easily wound by coils, which may prevent disconnection of the coils. PA1 (5) Since the spring 23 employed in the conventional cylindrical driving unit is no longer required, conventional problems could be solved, such as operation currents being adversely influenced by fluctuation in spring forces of spring 23, furthermore, smooth operations could not be achieved due to the sliding conditions of spring 23. PA1 (a) The driving unit may be assembled without using a screw. PA1 (b) It is possible to suppress an increase in the quantity of components employed in the light-amount controlling apparatus of the present invention. PA1 (c) The light-amount controlling apparatus of the present invention may be assembled at a place where no tools are available. PA1 (d) A total assembling stage of this light-amount controlling apparatus may be reduced, as compared with that of the conventional light-amount controlling apparatus. PA1 (e) The conventional problems of insufficient screwing works and loose screwing conditions could be solved.
On the other hand, when the galvanometer type driving unit is assembled, a large number of joint components such as screws are required. This assembly work must be carried out while picking up a large quantity of screws. Further various type of tools must be utilized. Therefore, there are the below-mentioned drawbacks: